A typical MCM package includes multiple layers of both dielectrics, such as polyimide, and conductors, such as copper. The die can be on the bottom, known as the die first case, or on the top, known as the die last case. The base substrate is usually ceramic in the die last case or silicon, in the die first case. In the die first case, the connection to the die is made directly by the thin film. In contrast, the chips are attached in the die last case via techniques such as wire bonding, solder balls, or stab bonding, or conductive adhesives.
There are several commonly used methods for fabrication of die first MCMs. One technique is to use an adhesive to attach the integrated circuits, I.C's, to a backing wafer. If the gaps between I.C.'s are large, either a stencil or some type of polymer fill material is used to fill the gaps between the I.C.'s. The thin film interconnect is built over the top of the I.C.'s, and the backing wafer becomes an integral part of the module. Others have used a method in which the I.C.s are attached to glass substrates with a heat releasable adhesive.
There are several disadvantages to the foregoing techniques. The carrier substrate is not reusable, which increases product costs. The carrier substrates tend to be relatively small, reducing the number of multi-chip modules that can be constructed on a single substrate. Production costs are related to the number of individual modules that can be put on a single substrate; therefore, having a small number of modules on a substrate increases the overall production costs. These techniques also require expensive semiconductor-processing equipment to handle wafers. By reducing the number of substrates handled, production labor costs are reduced. Use of integrated circuit processing chemicals increases the chemical costs related to processing. Thermal characteristics of prior techniques are undesirable because the integrated circuit is insulated by the carrier substrate.
Thus, there is a need for novel methods that are useful for producing MCMs in volume at lower cost.
There is a further need to provide novel methods that can allow the substrate to be used again to make another set of MCMs.
There is a further need to provide novel methods that can accommodate a large panel allowing a larger quantity of MCMs to be built on a single substrate.
There is a further need to provide novel methods that can allow for increasing the number of modules per substrate thus reducing the overall production cost per substrate.
There is a further need to provide novel methods that allow for the use of printed circuit board (PCB) equipment for the photolithography and metal patterning operations to reduce cost.
There is a further need to provide novel methods that can manufacture a MCM that has better thermal characteristics because the electronic components such as integrated circuits are not insulated by the carrier substrate.